1. Technical Field
Embodiments of the disclosure relate to semiconductor devices.
2. Related Art
Semiconductor devices may be typically categorized as either volatile memory devices or nonvolatile memory devices. The volatile memory devices lose their stored data when their power supplies are interrupted. In contrast, the nonvolatile memory devices retain their stored data even when their power supplies are interrupted. The nonvolatile memory devices may include various memory cells. For example, the nonvolatile memory devices may be classified into flash memory devices, ferroelectric random access memory (FRAM) devices, magnetic random access memory (MRAM) devices, phase change random access memory (PRAM) devices or the like according to a memory cell structure.
The flash memory devices among the nonvolatile memory devices may be categorized as either NOR-type flash memory devices or NAND-type flash memory devices according to a memory cell array scheme. All of memory cell transistors of the NOR-type flash memory devices are directly connected to bit lines and word lines in parallel. Thus, the NOR-type flash memory devices may exhibit a relatively fast random access time. In contrast, each of the NAND-type flash memory devices includes a plurality of cell strings connected to bit lines in parallel, and each cell string includes a plurality of memory cell transistors which are connected in series. That is, each cell string is electrically connected to a bit line through a single bit line contact. Thus, the NAND-type flash memory devices may exhibit a relatively high integration density.